Multimedia traffic including voice or video requires high quality for factors such as delay, jitter of delay or packet delivery ratio. Therefore, in order to relay such traffic in priority to other traffic (for example, text or image-downloading), techniques such as admission control (dynamic reservation of resources), classifier (classification of traffic), shaping and policing (keeping the burst to a defined level), and packet scheduling (transmitting the packet that corresponds to each group) are required.
The IEEE 802.11e protocol targeting single-cell wireless LANs (Local Area Networks) is being developed in order to control QoS (Quality of Service) of multimedia traffic.
The IEEE 802.11e provides functions of admission control, classifier, and packet scheduling for IEEE 802.11 wireless networks operating in infrastructure mode.
An infrastructure mode network includes an Access Point (AP) and a wireless LAN terminal (STA: Station). The wireless LAN terminal is provided within a communicable range from the Access Point AP.
The IEEE 802.11e protocol classifies traffic according to required levels of QoS (into four Access Categories of traffic provided in the IEEE 802.11e: AC1 (an AC for voice traffic), AC2 (an AC for video traffic), AC3 (an AC for best-effort traffic), and AC4 (an AC for background traffic)). Then, the IEEE 802.11e protocol gives priority channel access to traffic of an Access Category with higher priority according to the EDCA (Enhanced Distributed Channel Access).
In controlling the admission, transmission of voice traffic or video traffic requiring high QoS is allowed to the loads that the network is able to support in order to guarantee the quality of allowed multimedia communications. In other words, in order to guarantee the quality of allowed traffic, voice traffic and video traffic requiring transmission through the Access Categories AC1 and AC2 are allowed to the loads that the network capacity allows. More specifically, in a network that operates in admission control mode, a STA requesting transmission of voice traffic and video traffic transmits its admission request to an AP. In response to the admission request, the AP grants the admission if it determines that the network's capacity is able to meet the traffic's QoS request, and if not, the AP rejects the admission. Voice traffic (or video traffic) whose admission has been granted is transmitted through the Access Category AC1 (or AC2).
On the other hand, transmission of voice traffic (or video traffic) whose admission has been rejected is either cancelled or transmitted through the Access Category AC3 of best-effort traffic with lower priority. As described above, the IEEE 802.11e protocol provides techniques for controlling QoS over wireless communications.    Non-patent Document 1: IEEE P802.11e/D13.0, January 2005, (Draft Amendment to ANSI/IEEE Std 802.11, 1999 Edition (Reaff 2003)), Medium Access Control (MAC) Quality of Service (QoS) Enhancements.